This invention relates to the electrical measurement art, and more particularly to a new and improved sensor for electrostatic voltmeters.
An instrument which measures electrostatic fields and electrostatic potentials on surfaces without current flow through the instrument is known as an electrostatic voltmeter which makes measurements in a non-contacting manner. These instruments comprise a probe or sensor assembly and an associated voltmeter wherein the probe converts the electrostatic field or surface potential to an a.c. voltage, the magnitude of which is proportioned to the field or potential being measured. This conversion is accomplished by a capacitance modulation process wherein the capacitive coupling between a surface associated with the probe and a surface associated with the field or potential to be measured is modulated or varied at a fixed periodic rate. A voltage difference existing between the two surfaces will induce an a.c. voltage on the probe surface.
In some prior art electrostatic voltmeters unwanted drift and noise can result from dynamic coupling of the detector element to surfaces other than the test surface, especially when such other surfaces are contaminated. In some prior art apparatus, moving the detector element closer to the test surface increases capacitive loading of the test surface by other elements of the sensor. Also, some prior art apparatus is easily damaged by shock or impact and the detector thereof cannot be exposed to extreme temperature or pressure conditions due to the potentially adverse effects of such conditions on other components of the instrument.